The PowerBlock® is a well known selectorized dumbbell manufactured and sold by Intellbell, Inc. of Owatonna, Minn. In such a dumbbell, a plurality of weights are provided that form a set of nested left weight plates and a set of nested right weight plates. The two sets of nested weight plates are laterally separated from one another by a space or gap. A handle can be inserted or dropped down into the gap to allow the handle to pick up a desired number of weight plates from each stack. The amount of the exercise mass provided by the selectorized dumbbell depends upon how many weight plates from each stack are coupled to each end of the handle.
In the PowerBlock® selectorized dumbbell, each weight comprises a left weight plate that is integrally joined to a corresponding right weight plate by a pair of side rails. The side rails are welded at each end to one side of each weight plate. One side rail is welded to the front sides of the left and right weight plates. The other side rail is welded to the rear side of the left and right side plates.
FIG. 3 of this application shows a single weight from the PowerBlock® selectorized dumbbell. The weight is formed by a joined pair of weight plates with only the front side rail being shown in FIG. 3, the rear side rail being hidden on the other side of the weight plates in FIG. 3. The weight plates in different weights are spaced further apart and the side rails used to join these weight plates together are correspondingly longer and vertically offset. This permits the nesting of the weight plates together in their respective left and right stacks of weight plates.
The selector in the PowerBlock® selectorized dumbbell comprises a pin that may be selectively positioned beneath the side rails of any desired weight. Thus, when the selector is so positioned and the handle is lifted, the handle will carry with it the weight selected by the position of the pin along with all weights above the selected weight. The amount of the weight carried by the handle is adjusted by vertically repositioning the pin so as to insert the pin beneath a higher or lower side rail.
In the past, certain models of PowerBlock® selectorized dumbbells have used ½″ stamped steel plates as the weight plates in manufacturing the individual weights. Such ½″ weight plates typically have significant manufacturing imperfections along the edges thereof. These imperfections include burrs, rough spots, and the like, formed by the edges of the stamping die when the weight plates are stamped out of ½″ steel stock. Thus, it was necessary to use a CNC milling machine to mill the edges of such ½″ weight plates to remove such imperfections and in doing so the ½″ weight plates were provided with curved edges along all four sides thereof.
FIG. 5 shows in phantom the roughly rectangular edges of the ½″ weight plate as it came out of the die and in solid the curved edge formed by the milling step. Obviously, the material between the curved edge and the phantom line rectangular edge represents the material removed during the milling step. In addition, each ½″ weight plate also had a pair of mounting holes stamped through each plate in order to secure the plate to the milling machine used in the milling operation. Such holes also represent a significant loss of material from each ½″ weight plate.
After the edges of the ½″ weight plates were milled as described above, two such plates were then inserted into a welding fixture at whatever spacing was appropriate to the weight being manufactured. The two side rails for this weight were then welded to the weight plates at generally identical heights along the front and rear sides of the weight plates to join the weight plates together. The weight plates and side rails were then cleaned of debris and contaminants by spraying them with a cleaner. Finally, the weight formed by the weight plates and the side rails went through a powder coating process to apply a finish coating to the side rails and to both sides of the weight plates.
While this is an effective way to manufacture weights for selectorized dumbbells, it does involve labor in terms of milling the edges of the weight plates to make them sufficiently smooth to be acceptable. In addition, given recent price increases for ½″ steel stock, the prices for obtaining ½″ stamped steel plates has dramatically increased. This forces the manufacturer of selectorized dumbbells to either increase prices, which is not favored by the purchasers of such dumbbells, or to make less margin on the product, which is not favored by the manufacturer. A simpler and less expensive way to manufacture selectorized dumbbell weights would be an advance in the art.